Grain loss is a significant process factor when operating combine harvesters. Grain loss can be used in selecting travel speed and adjusting the parameters of the threshing process. However, it is difficult to precisely calculate grain loss from an operating combine harvester.
Devices for measuring grain loss are currently installed in almost all combine harvesters. However, their accuracy is deficient. There has been no satisfactory technical solution up to the present for a long-lasting and sufficiently accurate determination.
The known measuring devices for grain losses generally consist of several grain sensors that are arranged below the working parts such as threshing cylinders, straw walkers, sieves, etc., and that furnish signals when grain strikes. The more frequently the grain strikes, the higher the grain losses.
However, it cannot be precisely determined which portion of the grains that are collectively present in the crop flow is measured and how many grains furnish a direct electric impulse and which portion is not measured, since it does not initiate an electric impulse. The result can be additionally falsified by straw nodes, that also initiate electric impulses.
It has been determined that all previous solutions therefore contain the same system-conditioned measurement errors. The impulse frequency is a direct function only of the amount of grain in the lowest layer of the straw mat and is additionally influenced by changing harvesting conditions. What amount of grain is present in the layers above this lower layer cannot be determined. In the case of unfavorable separating conditions, the ratio between impulse-initiating grain and the total grain loss in the straw mat located above the impulse-initiating grain is smaller than under more favorable conditions. As long as the quantitative distribution of grain in the straw mat located above the impulse-initiating grain cannot be determined, no exact measurement of losses is given by the sensor systems measuring on the bottom of the straw mat. Arranging of sensors directly in the crop flow of the combine harvester and/or an identification of grain in the straw mat with physical measuring principles is not possible.
It appears obvious, e.g., to use several sensors for determining the characteristic separating line. However, the occurrence of the above-cited error in all sensors is again a disadvantage, so that the measuring accuracy could not be substantially increased. The quantitative distribution of grain and the straw mat continues to be unknown.
Measuring devices that detect the throughput of harvested crop and that have erroneous measured values are also located at other positions in harvesting machines, especially in combine harvesters. In order to reduce measuring errors U.S. Pat. No. 5,369,603 teaches calibrating an impact plate sensor with test runs in which the mass of the harvested grain tank content is measured by weighing. DE 195 41 177 A suggests measuring the crop flow continuously with a first measuring device. The crop flow is subsequently transported into a second measuring device whose measured value is used to calibrate the first measuring device. As defined by both publications a measured value is first detected with a first sensor and the measured value of the first sensor is subsequently calibrated with a second sensor. However, two sensors are required for this.